Dielectric constants of Ir, Ru, Pt, and IrO2:: Contributions from bound charges

We investigated the dielectric functions epsilon(omega) of Ir, Ru, Pt, and IrO2, which are commonly used as electrodes in ferroelectric thin-film applications. In particular, we investigated the contributions from bound charges epsilon(b)(omega), since these are important scientifically as well as technologically: the epsilon(b)(1)(0) of a metal electrode is one of the major factors determining the depolarization field inside a ferroelectric capacitor. To obtain epsilon(b)(1)(0), we measured reflectivity spectra of sputtered Pt, Ir, Ru, and IrO2 films in a wide photon energy range between 3.7 meV and 20 eV. We used a Kramers-Kronig transformation to obtain real and imaginary dielectric functions, and then used Drude-Lorentz oscillator fittings to extract epsilon(b)(1)(0) values. Ir, Ru, Pt, and IrO2 produced experimental epsilon(b)(1)(0) values of 48 +/- 10, 82 +/- 10, 58 +/- 10, and 29 +/- 5, respectively, which are in good agreement with values obtained using first-principles calculations. These values are much higher than those for noble metals such as Cu, Ag, and Au because transition metals and IrO2 have such strong d-d transitions below 2.0 eV. High epsilon(b)(1)(0) values will reduce the depolarization field in ferroelectric capacitors, making these materials good candidates for use as electrodes in ferroelectric applications.